5970s Crossfired on a 750w PSU

[st4rdust]

I know I'm cutting it awfully close here. The PSU in question is a PC Power and Cooling 750w unit, with said GPUs to be hanging on a single 12v rail @ 60a.

http://www.newegg.com/Product/Product.aspx?Item=N82E16817703009

I also plan on overclocking these units as much as I can on stock cooling. I'd possibly put water blocks on each GPU in the future.

Anyway, as I said I know I'm cutting it close here. Anybody have experience crossfiring 5970s on similar wattage? Am I safe here or do I add something like this supplemental supply?

http://www.newegg.com/Product/Product.aspx?Item=N82E16817104054

I'd also think that for the price of that supplemental PSU, I might as well just spend the few extra bucks to get something like PC P&C's 910w unit.

http://www.newegg.com/Special/ShellShocker.aspx?cm_sp=ShellShocker-_-17-703-022-_-10012011_2

Thanks for your input!

EDIT: Oops, probably should mention what the rest of my system contains. Intel Core i7 920 at stock volts/clock on a Gigabyte x58 board with 3x4gb DDR3 RAM @ 1.5v. 3 x 640gb WD 7200RPM HDDs in RAID0. Four 120mm LED fans and two 60mm fans mounted in a PCI slot, powered by 4pin Molex, to cool GPU.

[1714194680]

1714194680

[1714194680]

1714194680

[1714194680]

1714194680

[1714194680]

1714194680

[DeathAndTaxes]

It would be incredibly close.

You really shouldn't load powersupply >80% of sustained load rating.  Efficiency suffers (more electric bill), it runs hotter (greater % of electrical power wasted as heat), and ultimately it is very hard on the components (reduces average power supply life).

Still you likely can get away with it.  I have a 3x 5970 rig.  I just shutdown one of the card and load is 710W.  That is for 2x 5970 clocked @ 870/300.  Real load is 30W lower because the 3rd 5970 will be idle and it draws ~30W when idle.

So ~680W AC @ 85% efficiency = ~580W DC.  Certainly do-able on 750W IF the manufacturer rating is valid.

[st4rdust]

So ~680W AC @ 85% efficiency = ~580W DC.  Certainly do-able on 750W IF the manufacturer rating is valid.

Thanks a lot for your response. I've always held PC Power and Cooling PSUs in high regard and will usually make a point to put these into my systems whenever building a performance-oriented machine. PCP&C units have always held up for me in these close-cut type situations, where other lesser-quality brands have failed (most recently, my Apevia Java 650w unit let out a loud pop - it died completely under the load of merely one 5970 and a 5770 in an otherwise very tame and baseline system). From my first build, they've never done me wrong so I have a trust for these PSUs. This one I'm using is from a 2008 build and it still has over 2 years left on the original warranty!

You mentioned your GPUs are clocked at 870/300. Is this on air and stock volts? I would be looking to OC my 5970s to max on air but with extra voltage, which is why I'm concerned about the PSU. If yours are overvolted too, it seems like (from what your power draw is) the dual-5970 overvolt crossfire may just hold up for my PSU.

[jjiimm_64]

interesting subject for me. 

I have 2 rigs with 4 5970's.  one of them has 2 psus, no harddrive.  pulling 1200 watts at the wall clocked at 820/420 getting 2900 Mh stable.

I am purchasing some 750 watt SeaSonics to build more of these rigs. will put 2 psus per rig. hoping to get the same efficiency as I am with the 2 1200 watt psus I have in the current rig.

https://picasaweb.google.com/112408294399222065988/October12011

[DeathAndTaxes]

You mentioned your GPUs are clocked at 870/300. Is this on air and stock volts? I would be looking to OC my 5970s to max on air but with extra voltage, which is why I'm concerned about the PSU. If yours are overvolted too, it seems like (from what your power draw is) the dual-5970 overvolt crossfire may just hold up for my PSU.

No they are watercooled (running @49.5C to 52C today).  I should say 5 of the card are @ 870 and 1.162V.  The last card (used for desktop) is running @ stock.  For some reason I can't get it stable if using the desktop on anything beyond stock.  I have tried every voltage/speed combination.  I am tempted to buy an cheap single slot graphics card w/ dual DVI to connect my monitors to so I can max out that last 5970.

[st4rdust]

In the end, I decided that it wasn't worth it to me to put that PSU at risk. Luckily, last week Newegg ran as part of its daily "shell shocker" deals, a 910w PC Power & Cooling Silencer unit for $109. This deal came along at the perfect time for me, so when it arrives within the next couple of days I won't break a sweat when plugging in my dual 5970s, knowing I'm well within my power budget.

Anyone else happen to catch the 910w Silencer discount??

[jjiimm_64]

Well,  I can tell you that I have 4 5970's running with 2 750 watt Seasonics.  I am pulling 1180 watts from the wall.  I would say that my efficiency has not suffered.

[d.james]

One of my mining rig has 1x 5970, 1 x 5870, and 1x 5850.

So technically my rig uses more power than 2x 5970, and it's pulling around 710-730W from the wall.

A 750W might work if you don't OC, for me, I'm using a 1000W PSU to be safe.

[jjiimm_64]

do not skimp on psu, it is the most important piece of the puzzle.

all of my single psu rigs are 1200 psus.   why push a psu to its absalute limit, for that matter the gpus also.  everything will last alot longer if it is run at 75% full  (gpu, psu, your car, my plane, anything.)

[m3sSh3aD]

do not skimp on psu, it is the most important piece of the puzzle.

all of my single psu rigs are 1200 psus.   why push a psu to its absalute limit, for that matter the gpus also.  everything will last alot longer if it is run at 75% full  (gpu, psu, your car, my plane, anything.)

+1 I use Antec 1200W HCP on 4x5850 rigs and thats because they had no Corsair AX1200 in. Each card is using about 115amps at 1000/300 so i have them at 965/300 cause the PSU is rated at 98amp. Corsair is 100amp and single rail. There truely the best PSU'd on the market. When looking in 700-800 your options are HUGE but if you stick with Corsair AX series (you may tell that i reccommending these supplys) you cant go wrong. Only thing you have to pay good money for is PSU, VGA cards and COOLING!!!

@jjiimm_64 - Off topic, but hows the wall street thing going, I've heard about it all and it was on the radio the other day Its spreading, thats what they were on about

[sveetsnelda]

In case you aren't aware, almost all of the PC Power & Cooling PSUs are just rebadged Seasonic units.  The older ones were made by Sparkle.

Seasonic makes incredible PSUs.  A 750 watt Seasonic would easily take care of two 5970s.  If you were *heavily* overclocking them, you'd probably hit a significant efficiency threshhold on the PSU though.

My i7 920 box with two 5970s draws 713 watts while mining at 820/300 with the voltage slightly dropped to 1.037.  The box has a Vertex 2 SSD and 6 DIMM modules.  This is pretty similar to your setup.

[jjiimm_64]

@jjiimm_64 - Off topic, but hows the wall street thing going, I've heard about it all and it was on the radio the other day Its spreading, thats what they were on about

I only know what I hear on the radio...  I gave some btc to the cause, I think that would be a big deal if the media reported on that.  I dont think the protest is quite ready to adopt a new currency. at first it did sound good tho.

[m3sSh3aD]

@jjiimm_64 - Off topic, but hows the wall street thing going, I've heard about it all and it was on the radio the other day Its spreading, thats what they were on about

I only know what I hear on the radio...  I gave some btc to the cause, I think that would be a big deal if the media reported on that.  I dont think the protest is quite ready to adopt a new currency. at first it did sound good tho.

yes, thats in the UK too so i wouldnt jump to conclusions so quick. I know over here after bailing the banks out (RBS) to the tune of 800 billion, Alot of people would embrace BTC if it was more accessable/usuable in everyday life. No offence to any US here but people over here are a little more aware and fed up which you can look up the riots no to long ago. The arab uprising rings true so dont think that over here is sitting down 30 minutes of your time but this explains the riots better than most i've seen

http://www.youtube.com/watch?v=IMvuoGji3yU&feature=player_embedded

On topic, Seasonic are quality PSU's, but id do my reseach on the specific Power and Cooling cause i believe they use a few different suppiers all the time. I've had some poor quality ones, i know that You can grab a bargain this way though